Chronic drug administration can produce allostasis, a maladaptive state related to drug tolerance. This proposal investigates nitrous oxide (N2O)-induced allostatic changes and the motivational consequences of being in an allostatic state. Allostasis refers to a disordered form of homeostatic regulation wherein a regulated variable, or one or more of its controlling determinants, persistently functions at levels significantly different from control values, potentially compromising an individual's health or viability. An allostatic model of drug addiction posits that biobehavioral control systems regulate variables relevant to drug taking behavior and that these control systems are vulnerable to drug-induced allostatic changes which promote the development of addiction. The proposed studies use a sophisticated experimental model that combines direct and indirect calorimetry so that core temperature and its determinants (metabolic heat production and heat release) can be simultaneously measured, enabling rigorous determination of allostatic dynamics during repeated N2O administrations. This thermoregulatory model system also provides a sensitive method for determining the motivational consequences of allostasis. Preliminary data indicate that adolescent rats are especially prone to develop drug-induced allostatic changes, suggesting that increased susceptibility to allostasis development may be a critical etiological factor for the heightened vulnerability to drug addiction during adolescence. Specific Aim (SA) 1 compares allostasis development in adolescent versus mature rats over a range of N2O concentrations, determines whether these allostatic processes stabilize, and explores how they can be extinguished. SA 2 compares the thermally motivated effects of a range of N2O concentrations in adolescent versus mature rats and assesses the motivational effects of an allostatic state during adolescence. In addition, the relationship between initial sensitivity, allostasis development and N2O self-administration behavior will be investigated. SA 3 examines whether factors measured in the allostatic state (N2O concentration, core temperature, heat loss, heat production) can be used as predictors of motivated behavior. This work has practical and theoretical importance for understanding the mechanisms underlying drug addiction. The proposed research has the added relevance of investigating an abusable inhalant during the adolescent period which NIH has identified as an important, yet understudied, research area. PUBLIC HEALTH RELEVANCE: A form of homeostatic dysregulation known as allostasis is suspected to play an etiologic role in the development of drug addiction. The proposed research uses an understudied inhalant to investigate drug-induced allostasis during a developmental period (adolescence) that is known for its heightened susceptibility to drug addiction. The findings of this research will contribute to our understanding of the pathogenesis and treatment of drug addiction. [unreadable] [unreadable] [unreadable]